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"NAEGA and NGFA are gravely concerned about the serious economic harm to exporters, grain handlers and, ultimately, agricultural producers – as well as the United States' reputation to meet its customers' needs – that has resulted from Syngenta's current approach to stewardship of Viptera," the groups wrote.

"Further, the same concerns now transcend to Syngenta's intended product launch plans for Duracade, which risk repeating and extending the damage. Immediate action is required by Syngenta to halt such damage."

While the groups were quick to point out that they support agricultural biotechnology, they said in the letter that "numerous negative consequences" could result when unapproved varieties make their way into export markets.

Some of the consequences, the groups said, include: a reduction in value and demand for U.S. farmers' products, increased cost of market access and diminished reputation of the U.S. as a reliable source of ag products.

Commercialization prior to foreign regulatory approvals also has a negative impact on the overall U.S. corn and other grain value chains, they said, and reduces U.S. agriculture's contribution to global food security and economic growth.

Paul Minehart, spokesman for Syngenta, told Ros Krasny and Tom Polansek of Reuters, however, that the real issue is synchronized approvals by grain importing countries. Further, a change of course, he said, wouldn't affect much.

"Changing our marketing plan in the U.S. now would have no effect on grain in the system or Chinese acceptance of corn imports," Minehart said.

But NGFA and NAEGA argue that the issue is pressing as farmers make 2014 planting decisions. The groups suggested that farmers check with local grain elevators and merchants to determine if there are any additional limitations on accepting biotech traits.

The National Corn Growers issued a similar request earlier this week, pointing farmers to its Know Before You Grow tool, an online resource that lists approval status of all major corn traits in export markets.